Bump version to 4.19.1

• Diff: https://gitlab.com/gitlab-org/gitlab-qa/compare/v4.19.0...48404030510b3b458b95f6839cf00e34e7dd621e

• Release notes:

### Fixes

- !381 Geo clusters need at least a db_pool value of 3

• Checklist before merging:

  • Diff link is up-to-date.
  • Based on the diff, lib/gitlab/qa/version.rb is updated, according to SemVer.
  • Release notes are accurate.

• Checklist after merging:

  • Create a tag for the new release version.